Operation indicator of a heater



FIG. 1 is a front view of an operation indicator of a heater showing my new design;

FIG. 2 is a rear view thereof;

FIG. 3 is a top plan view thereof;

FIG. 4 is a left side elevational view thereof;

FIG. 5 is a right side elevational view thereof; and,

FIG. 6 is a perspective view thereof.

The broken lines in FIGS. 1 through 6 are shown for illustrative purposes only and form no part of the claimed design. 

The ornamental design for an operation indicator of a heater, as shown and described. 